About one in six sudden infant deaths may be linked to their mothers' heavy alcohol use during or soon after pregnancy, according to a new study from Australia.

Researchers found those deaths may result from babies being exposed to alcohol in the womb and from alcohol-using mothers creating hazardous environments for the babies after birth.

"One of the morals of the story is that parents should be very careful about drinking alcohol, especially if you're a single parent because there is no other parent to back you up," said David Phillips, a professor at the University of California, San Diego, who has studied alcohol-related infant deaths but wasn't involved in the new research.

The US Centers for Disease Control and Prevention (CDC) defines sudden infant death syndrome (SIDS) - also known as sudden unexpected infant death - as the death of a child under one year old with no obvious cause.

Previously, researchers have tied SIDS to parents' smoking and to unsafe environments, but few studies have looked at whether alcohol could be involved in some of the deaths.

For the new study, the researchers, led by Colleen O'Leary from Curtin University in Perth, examined information on 77,895 women who gave birth between 1983 and 2005.

They compared the number of SIDS and infant deaths that occurred in children of mothers with a diagnosed drinking problem, to cases among the children of mothers without a diagnosis.

Overall, 171 SIDS cases occurred during that time in children born to the 21,841 women who were diagnosed heavy drinkers. Among the children who were born to 56,054 mothers without a diagnosis, there were 132 SIDS cases.

The researchers found that babies born to mothers who drank heavily during pregnancy had a seven-fold increase in the risk of SIDS, compared to children of mothers without a drinking problem.

Babies also had a nine-fold increased risk of SIDS when their mothers drank within the year after birth, compared to babies born to mothers who didn't drink.

O'Leary, who could not be reached for comment, and her colleagues also report that heavy drinking during pregnancy was tied to a doubled risk of infants dying from a cause unrelated to SIDS, compared to babies of mothers who were not heavy drinkers.

"The results of this study indicate that maternal alcohol-use disorder increases the risk of SIDS and (infant deaths) through direct effects on the foetus and indirectly through environmental risk factors," the team wrote in the journal Pediatrics on Monday.

The authors add that previous research suggests babies exposed to alcohol in the womb may have abnormalities in the brainstem, which could lead to problems regulating basic body functions like breathing.

But Phillips pointed out that the study found a link between infant deaths and a mothers' drinking as long as one year after giving birth.

"So it can't just be a biological explanation of what's going on," he said.

The mothers may be creating unsafe environments for their children, Phillips said. For example, a drunken parent may fall asleep with their baby in bed, and accidentally roll over and suffocate the child.

O'Leary's team writes that it found a number of causes for the children's deaths, including problems related to alcohol exposure in the womb and environmental factors - such as smoke inhalation, dehydration, infections and neglect.

The researchers suggest that preventing heavy drinking in mothers may bring the number of SIDS cases and infant deaths down.

A separate study, also published Monday in Pediatrics, found that doctors can use visualisation and mapping software to identify babies who have slight facial deformities that may signal mental impairments from their mothers' drinking.

Phillips said it's also important for parents to understand that it only takes a couple drinks for their judgment to become impaired, and parents who plan to have a drink should have a sober "designated parent" to care for their child.

"A child is a vulnerable creature and we really owe it to protect that child. It's not a trivial thing to be a parent," he said.